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displayed_sidebar: "Chinese"
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# days_sub

## 功能

从给定日期或者日期时间中减去指定的天数，获得新的 DATETIME 结果。

## 语法

```Haskell
DATETIME days_sub(DATETIME|DATE date, INT n);
```

## 参数说明

`date`: DATE 或者 DATETIME 类型的表达式。

`n`: 要减去的指定天数。

## 返回值说明

返回一个 DATETIME 类型的结果。

如果任一参数为 NULL 或者不合法，则返回 NULL。

当计算结果超出 [0000-01-01 00:00:00, 9999-12-31 00:00:00] 的范围，则返回 NULL。

## 示例

```Plain Text
SELECT DAYS_SUB('2022-12-20 12:00:00', 10);
+--------------------------------------------------+
| days_sub('2022-12-20 12:00:00', INTERVAL 10 DAY) |
+--------------------------------------------------+
| 2022-12-10 12:00:00                              |
+--------------------------------------------------+

SELECT DAYS_SUB('2022-12-20 12:00:00', -10);
+---------------------------------------------------+
| days_sub('2022-12-20 12:00:00', INTERVAL -10 DAY) |
+---------------------------------------------------+
| 2022-12-30 12:00:00                               |
+---------------------------------------------------+

SELECT DAYS_SUB('2022-12-20 12:00:00', 738874);
+------------------------------------------------------+
| days_sub('2022-12-20 12:00:00', INTERVAL 738874 DAY) |
+------------------------------------------------------+
| 0000-01-01 12:00:00                                  |
+------------------------------------------------------+

SELECT DAYS_SUB('2022-12-20 12:00:00', 738875);
+------------------------------------------------------+
| days_sub('2022-12-20 12:00:00', INTERVAL 738875 DAY) |
+------------------------------------------------------+
| NULL                                                 |
+------------------------------------------------------+

SELECT DAYS_SUB('2022-12-20 12:00:00', -2913550);
+--------------------------------------------------------+
| days_sub('2022-12-20 12:00:00', INTERVAL -2913550 DAY) |
+--------------------------------------------------------+
| 9999-12-31 12:00:00                                    |
+--------------------------------------------------------+

SELECT DAYS_SUB('2022-12-20 12:00:00', -2913551);
+--------------------------------------------------------+
| days_sub('2022-12-20 12:00:00', INTERVAL -2913551 DAY) |
+--------------------------------------------------------+
| NULL                                                   |
+--------------------------------------------------------+
```

## 关键字

DAY,day
